As a substrate for print wiring/ laminated plates produced by impregnating a fiber sheet (e.g., woven fabrics, non-woven fabrics or paper of glass fiber) as a reinforcing material with a thermosetting synthetic resin (e.g., epoxy resins or polyimide resins) to produce a prepreg, laminating a plurality of prepregs as produced above, placing a metal foil on each of the both surfaces of the laminate, and then hot pressing the assembly are widely use.
A circuit wiring is formed on the metal foil on each of the both surfaces of the substrate by the photoresist method, and a solder resist cured pattern is further provided thereon by the photoresist method to produce a print wiring plate.
As the solder resist, ultraviolet light-curable resists (e.g., acrylic compound-modified epoxy resins having excellent physical properties) are used. In order to obtain a resist cured pattern by irradiating the both surfaces with an ultraviolet light at the same time, it is required that the above-described glass fiber-reinforced synthetic resin substrate itself does not transmit therethrough an ultraviolet light. In order to obtain a glass fiber-reinforced laminated plate which shields an ultraviolet light, a method in which an organic ultraviolet light absorber is compounded into an impregnating resin varnish in the production of prepregs for glass fiber sheet (cf. JP-A-62-37822) and a method in which fine particles of titanium oxide are attached to a glass fiber sheet (cf. JP-A-62-28241) have been proposed. The term "JP-A" as used herein means an "unexamined published Japanese patent application".
In the method for obtaining ultraviolet light-shielding substrates, means for compounding an ultraviolet light absorber into a resin varnish for production of prepregs involves problems that satisfactory ultraviolet light-shielding properties are difficult to obtain even if a relatively large amount of the ultraviolet light absorber is compounded, curing properties of the varnish are readily reduced, and that the substrate is colored yellow. The method in which fine particles of titanium oxide are attached to the glass fiber sheet directly or after adding to a silane coupling emulsion involves problems that uniform dispersion stability of fine particles of titanium oxide is difficult to maintain and that since attachment of fine particles of titanium oxide often becomes uneven, it is necessary to attach the fine particles of titanium oxide in an amount more than the necessary amount for imparting the ultraviolet light-shielding properties, leading to whitening of the substrate.